THE QUANTIFICATION OF BIOEROSION IN FOSSIL CETACEANS OF THE PISCO FORMATION, PERU

The Pisco Formation (Miocene) in west-central Peru is known to contain numerous well-preserved and articulated whale fossils. The mechanism for such incredible preservation is still unknown. Preliminary observations have detected little, if any, scavenging of the bones by macro- or microfauna. This stands in contrast to modern examples where whale carcasses are rapidly affected by scavenging fauna within days of deposition. Within months to a few years even the bones have been destroyed. Our general research question is how so many of the fossil whales in the Pisco Formation avoided the bone scavenging that is normal now. This specific study was to identify and quantify micro-scale alteration of the bones.

Eighteen fossil whales from the Pisco Formation were excavated and sampled to survey for micro-erosion and other micro-scale alteration. Thin sections were examined for bioerosion, fractures and mineralogy. Crystallinity Index (CI) was also calculated from XRD for three of the whale specimens following Person’s (1995) methods.

Preliminary data show a complete lack of any microborings or other evidence of bioerosion of any type. The condition of these bones is in direct contrast to the condition of bones from modern-day whale falls and to those of other Miocene whale skeletons from Japan and Spain, all of which show extensive bioerosion and microborings. Diagenetic phases associated with the bones include anhydrite, dolomite, gypsum and manganese oxides and no evidence of pyrite.

Mineralogy suggests an oxidizing, marine environment. As expected the bones are fully mineralized. The absence of micro-scavenger and microbial artifacts points to an extremely rapid burial time of days to weeks.